In chapter 13

Physically Brian has shed any excess weight he had, tanned darkly from constantly being under the sun.But the biggest change, he realizes, is his mental change. His mind is different. He thinks and hears differently, recognizing the sounds of the forest and automatically knowing what they are before he even registers hearing them. He sees differently, too; when he looks at a bird he sees not just the bird as a whole, but every individual feather, its size and shape, all of those details. Whenever he hears a sound or sees a sight, he reflectively moves towards it, prepared to deal with whatever it is. He is changing.